1. Introduction
In recent years, mechanical splices (hereafter, called as couplers) are widely used in RC buildings; thus, RC beams without stirrups on couplers have many advantages in design and construction. This paper focuses on the shear strength of the above RC beams. The experiments preceded by the authors were outlined and simulated by three-dimensional nonlinear FEM analyses to discuss the shear-resisting mechanisms. Furthermore, based on the analytical findings, shear design equations proposed in the authors’ previous study were modified and verified.
2. Outline of the preceded experiments for analytical study
Four specimens with different details on couplers which were tested in the authors’ preceded study were outlined: a control specimen without couplers named NN1, and other three specimens having couplers with different lengths of 180 mm, 280 mm, and 380 mm named MI1, MI1A, and MI1B, respectively (Fig. 1 and Tables 1-3). These specimens were designed assuming a specific shear failure mode with compressive failure of concrete. As a result, the maximum strengths of NN1 and MI1 were similar to each other, while those with longer couplers were lower compared to NN1 and MI1 (Fig. 4).
3. Three-dimensional nonlinear FEM analysis
Three-dimensional nonlinear FEM analyses were conducted using FINAL Ver. 11 for four experimental specimens and four additional ones with longer couplers (Fig. 5). Core and cover concrete was modeled using eight-node isoparametric solid elements, and longitudinal bar and stirrup were modeled using two-node truss elements. Coupler was modeled using eight-node isoparametric solid elements to reproduce bearing pressure at coupler ends (Fig. 6).
4. Analytical results
The shear force-drift angle relationships of four experimental specimens were compared with the test results (Fig. 8). The analytical results agreed well with the experimental ones; thus, differences in the maximum strengths were limited at -6% to +4%. Major findings are summarized as follows:
[Effects of the presence or absence of couplers] The averaged stress of stirrups was lower in MI1 (Fig. 9), while the maximum strengths and minimum principal stress distributions were similar to each other. It indicated that the shear-resisting mechanisms might be different between NN1 and MI1.
[Effects of coupler length] In the cases with longer couplers, the truss mechanism deteriorated but the arch mechanism remained in the ultimate states (Fig. 10).
5. Modification of design equations for the shear strength of RC beams of interest
Based on the above analytical results, the shear design equations of RC beams without stirrups on couplers were modified considering 1) existence of arch mechanism remaining after deterioration of truss mechanism by Eq. (7), and 2) confinement to core concrete along couplers by Eq. (9).
6. Verification of the proposed modifications
The modified shear design equations were verified comparing with the experimental results of seventeen RC beam specimens from the authors’ previous study. Consequently, a better agreement was obtained between the test results and the estimations considering the modifications (Fig. 20). The average and coefficient of variation on the experimental value/calculated value were 1.29 and 18.4%.
抄録全体を表示